Strand anchor

ABSTRACT

A strand anchor, especially for use in mining, comprising a strand having several wires, an anchor head, an anchor plate supported by the anchor head for placement onto the rock, should make it possible to discharge the displaced air when the curable material is being injected into a drilled hole, without the need for a separate hose. At least one longitudinal channel, preferably a plurality of longitudinal channels, is/are formed between the wires of the strand, so that air can be discharged to the outside through the strand through the at least one longitudinal channel when the curable material is being injected into a drilled hole.

This claims the benefit of German Patent Application DE 10 2011 078 767.4, filed Jul. 7, 2011 and hereby incorporated by reference herein.

The present invention relates to a strand anchor, and to a method for setting a strand anchor.

BACKGROUND

Strand anchors are employed in mining and tunnel digging in order to prevent and to slow rock movement of the bedrock, or to secure large-scale spalling of the bedrock, so as to allow safe operation. The strand anchor is adhesively bonded to a curable material, for instance, mortar or synthetic resin, and then set in a hole that has been drilled into the bedrock.

After a hole has been drilled into the rock, a strand of the strand anchor is inserted into the drilled hole, after which curable material is injected into the drilled hole through the entrance of the hole. In this process, the curable material displaces the air that is in the drilled hole, and the air is then discharged through an injection or venting line. For this purpose, not only the strand, but also the injection and venting line has to be inserted into the drilled hole, so that the air can be discharged from the drilled hole while the curable material is being injected into the drilled hole through its entrance. This is a drawback since a separate injection and venting line has to be provided and inserted into the drilled hole along with the strand. It is disadvantageous that the venting line ends at places where the venting does not really have to take place, so that an air pocket can remain in the drilled hole after the curable material has been injected. Moreover, it is necessary to drill a larger hole and this involves more drilling work since the strand anchor requires not only the strand but also the injection and venting hose.

U.S. Pat. No. 5,738,466 discloses a strand anchor consisting of several wires.

International patent application WO 2008/128301 A1 discloses a strand anchor having a strand that consists of several wires.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a strand anchor with which the air that is displaced when the curable material is injected into the drilled hole can be discharged from the hole without the need for a separate hose.

The present invention provides a strand anchor, especially for use in mining, comprising a strand having several wires, an anchor head, especially with an anchor nut, an anchor plate supported by the anchor head for placement onto the rock, whereby at least one longitudinal channel, preferably a plurality of longitudinal channels, is/are formed between the wires of the strand, so that air can be discharged to the outside through the strand through the at least one longitudinal channel when curable material is being injected into a drilled hole.

A plurality of longitudinal channels are present on the strand of the strand anchor between the wires, whereby the strand is configured as a central strand. When the curable material is injected into the drilled hole, the displaced air can be discharged from the drilled hole through these longitudinal channels. This advantageously means that the strand anchor does not have to have an injection or venting line. As a result, it is advantageous that the diameter of the drilled hole can be dimensioned considerably smaller since essentially only the strand needs to be accommodated in the drilled hole, thus translating into less drilling work. Moreover, there is likewise no need for a complex procedure to provide an injection or venting line when the strand anchor is being inserted.

In particular, the strand comprises wires having different diameters, especially with a diameter difference of at least 10%, 20% or 30%. The longitudinal channels are delimited by the wires of the strand so that, if the diameters of the wires are different, the wires delimit the longitudinal channels with a different curvature radius.

In another embodiment, the wires are configured with an essentially circular cross section and lie on each other, so that each longitudinal channel is delimited by wires, preferably by three wires, and/or the cross-sectional surface area of the flow or the sum of the cross-sectional surface areas of the flow of the at least one longitudinal channel is/are at least 0.1 mm², 0.5 mm², 1 mm², 2 mm², 5 mm² or 10 mm².

In a supplementary embodiment, the strand has a plurality of longitudinal channels, especially at least 5, 10, 20 or 30 longitudinal channels.

Preferably, several individual wires are held concentrically with respect to the strand by means of at least one spacer. Preferably, the strand anchor comprises several spacers, and the individual wires are held by the spacer at a distance from the strand which is thus configured as a central strand. In this context, the individual wires between the spacers can preferably always be at an essentially constant distance to the strand which is configured as a central strand, or else they can lie between the spacers on the strand which is configured as a central strand.

In a variant, the individual wires are arranged at a distance from the strand.

In a supplementary variant, the spacer is made of metal or plastic.

In an additional embodiment, the wires of the strand and/or the individual wires are made, at least partially, especially completely, of metal, particularly steel.

In an additional configuration, the strand and/or the individual wires are embossed or profiled on the outside. This enhances the mechanical connection or the adhesive bond between the curable material and the outside of the strand and preferably the individual wires.

A method according to the invention for setting a strand anchor, especially a strand anchor as described in this patent application, comprises the following steps: drilling a hole into the rock, inserting a strand of the strand anchor into the drilled hole, injecting curable material into the drilled hole in the area of its entrance, discharging from the drilled hole air that has been displaced by the curable material, whereby the displaced air is discharged from the drilled hole at least partially, preferably completely, through at least one longitudinal channel, preferably through several longitudinal channels, that are present in the strand.

In one variant, the air flows through a back end of the at least one longitudinal channel at a back end of the strand into the at least one longitudinal channel and through a front end of the at least one longitudinal channel at a front end of the strand, preferably outside of the drilled hole.

Advantageously, the air also flows radially outside of the back end into the longitudinal channels in the strand.

In another embodiment, after the curable material has been injected into the drilled hole, the curable material is brought into contact with the outside of the strand and preferably with the outside of the individual wires, so that a mechanical connection is established between the strand and preferably the individual wires after the curable material has cured.

In particular, after the curable material, for instance, mortar or synthetic resin, has cured, a tensile force is applied to the strand and preferably to the individual wires by means the pre-tensionable anchor head, preferably via its anchor nut. The anchor head applies a compressive force onto the rock in the area of the entrance of the drilled hole, thus stabilizing the outer strata of rock, and this compressive force is introduced as a tensile force into the strand and, from the strand, it is transmitted adhesively with the curable material to the rock in the area of the drilled hole.

Another preferred embodiment of the invention lies in the fact that, after the hole has been drilled and before the strand has been inserted, a cartridge containing another curable material is inserted into the drilled hole. According to this embodiment, the strand is anchored in the drilled hole with a short cartridge before the pressing procedure, after which the rest of the drilled hole is filled with curable material. Consequently, especially the following sequence is conceivable: 1) drilling, 2) inserting the cartridge into the drilled hole, 3) inserting the strand anchor into the drilled hole, 4) mixing the curable material contained in the cartridge by means of the strand anchor, 5) curing the curable material contained in the cartridge, whereby the strand anchor is pre-anchored in the drilled hole, 6) tensioning the strand anchor and 7) injecting the curable material into the drilled hole in the area its entrance and concurrently conveying out of the drilled hole the air displaced by the curable material, whereby the displaced air is discharged from the drilled hole at least partially through at least one longitudinal channel in the strand. The curable material contained in the cartridge can especially have different characteristics from those of the curable material that is injected in the area of the entrance of the drilled hole. For instance, the material contained in the cartridge can be a two-component material and/or the material that is injected in the area of the entrance of the drilled hole can be cement.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will be described in greater detail below making reference to the accompanying drawings. The following is shown:

FIG. 1: a longitudinal section of a strand anchor that has been inserted into a hole that has been drilled into the rock, after the curable material has been injected into the space between the rock and the anchor tube;

FIG. 2: a cross section A-A of the strand anchor according to FIG. 1.

DETAILED DESCRIPTION

A strand anchor 1 is employed in mining in order to temporarily stabilize rock in tunnels. The strand anchor 1 is a chemical anchor, that is to say, a strand 2 of the strand anchor 1 is adhesively bonded to the rock 18 by means of a curable material 11, e.g. synthetic resin 12 or mortar 13. For this purpose, a hole 19 has to be drilled into the rock 18 and subsequently, the strand 2 of the strand anchor 1 is inserted into the drilled hole 19.

The strand anchor 1 comprises not only the strand 2 comprising a plurality of wires 3 made of steel and having different diameters but also seven individual wires 7 made of steel. Several annular spacers 8 made of plastic hold the individual wires 7 at a distance from the strand 2 that is configured as a central strand 2. According to the depiction shown in FIG. 1, the individual wires 7 are consistently held at an essentially constant distance between the spacers 8 with respect to the strand 2, so that the individual wires 7 do not touch the strand 2. The strand 2 has a back end 5 in the area of a back end of the drilled hole 19, and a front end 6 in the area of a work space 21 outside of the drilled hole 19. The strand 2 as well as the individual wires 7 are fastened to an anchor head 14 that is only schematically indicated here, whereby the anchor head 14 in the embodiment shown has an anchor nut 16 that is arranged on an anchor-head thread 15. The anchor nut 16 rests on an anchor plate 17.

After the hole 19 has been drilled into the rock 18, the strand 2 with the individual wires 7 as well as the spacers 8 are inserted into the drilled hole 19. After the strand 2, the individual wires 7 and the spacers 8 have been inserted, curable but not yet cured material 11 is injected into the drilled hole 19 in the area of its entrance 20. As a result of this injection of the curable material into the drilled hole 19, the curable material displaces the air that is in the drilled hole 19 and conveys it through the strand 2 through longitudinal channels 4 between the wires 3 of the strand 2 at a back end 5 of the strand 2 that is configured as a central strand 2, so that the air at the front end 6 of the strand 2 flows into the work space 21 and out of the drilled hole 19. When the curable material is injected into the drilled hole 19, it comes into contact with the outside 9 of the strand 2 and the outside 10 of the individual wires 7. As a result, after the curable material 11 has cured and after the curable material 11 has been completely injected into the drilled hole 19, an adhesive bond can be created between the cured material 11 and the outside 9 of the strand 2 and the outsides 2 of the individual wires 7 (FIG. 1). As a result, a compressive force can be applied by the anchor nut 16 via the anchor plate 17 onto the rock 18 in the area of the entrance 20 of the drilled hole. This compressive force is introduced as a tensile force into the strand 2 and into the individual wires 7, and subsequently introduced into the rock 18 at the drilled hole 19 due to the adhesive bond between the curable material 11 and the outside 9 of the strand 2 as well as the outsides 10 of the individual wires 7. An adhesive bond likewise exists between the curable material 11 and the rock 18 at the drilled hole 19.

All in all, considerable advantages are associated with the strand anchor 1 according to the invention. The strand anchor 1 does not require an injection or venting line since the displaced air that is in the drilled hole 19 can be discharged to the outside through longitudinal channels 4 in the strand 2. As a result, the diameter of the drilled hole 19 can be dimensioned considerably smaller, that is to say, it can essentially match the diameter of the strand 2 with the individual wires 7, thus translating into less drilling work. Moreover, there is no longer a need for a complex procedure to provide an injection or venting line.

In addition, due to the spaces which are created by the spacers 8 and through which the cement flows, the complete steel bundle comprising the strand 2 and the individual wires 7 has a larger surface area for the bonding than a conventional steel bundle of the same cross section.

An optional cartridge 100 with further curable material can be placed in the drilled hole 19 and is shown schematically. Cartridge 100 can be punctured by the strand anchor and temporarily hold the strand anchor before the curable material is injected. The amount or type of material in the cartridge can be such that the end 5 remains free of the further curable material so that air can still flow through end 5. 

1. A strand anchor comprising: a strand including a plurality of wires; an anchor head; an anchor plate supported by the anchor head for placement onto rock; the plurality of wires defining at least one longitudinal channel between the wires of the strand, the at least one longitudinal channel permitting air to be discharged to an outside through the strand through the at least one longitudinal channel when a curable material is injected into a drilled hole.
 2. The strand anchor as recited in claim 1 wherein the wires have different diameters.
 3. The strand anchor as recited in claim 2 wherein a first diameter of a first wire of the plurality of wires is at least 10% larger than a second diameter of a second wire of the plurality of wires.
 4. The strand anchor as recited in claim 3 wherein a first diameter of a first wire of the plurality of wires is at least 20% larger than a second diameter of a second wire of the plurality of wires.
 5. The strand anchor as recited in claim 4 wherein a first diameter of a first wire of the plurality of wires is at least 30% larger than a second diameter of a second wire.
 6. The strand anchor as recited in claim 2 wherein at least one of the following is present: the wires are configured with an essentially circular cross section and lie on each other, so that each longitudinal channel is delimited by the wires; and a cross-sectional surface area of a flow, or a sum of the cross-sectional surface areas of the flow, of the at least one longitudinal channel is at least 0.1 mm².
 7. The strand anchor as recited in claim 6 wherein a cross-sectional surface area of a flow, or a sum of the cross-sectional surface areas of the flow, of the at least one longitudinal channel is at least 0.5 mm².
 8. The strand anchor as recited in claim 7 wherein a cross-sectional surface area of a flow, or a sum of the cross-sectional surface areas of the flow, of the at least one longitudinal channel is at least 1 mm².
 9. The strand anchor as recited in claim 8 wherein a cross-sectional surface area of a flow, or a sum of the cross-sectional surface areas of the flow, of the at least one longitudinal channel is at least 2 mm².
 10. The strand anchor as recited in claim 9 wherein a cross-sectional surface area of a flow, or a sum of the cross-sectional surface areas of the flow, of the at least one longitudinal channel is at least 5 mm².
 11. The strand anchor as recited in claim 10 wherein a cross-sectional surface area of a flow, or a sum of the cross-sectional surface areas of the flow, of the at least one longitudinal channel is at least 10 mm².
 12. The strand anchor as recited in claim 6 wherein each longitudinal channel is delimited by three wires.
 13. The strand anchor as recited in claim 2 wherein the at least one longitudinal channel includes a plurality of longitudinal channels.
 14. The strand anchor as recited in claim 13 wherein the plurality of longitudinal channels includes at least 5 longitudinal channels.
 15. The strand anchor as recited in claim 14 wherein the plurality of longitudinal channels includes at least 10 longitudinal channels.
 16. The strand anchor as recited in claim 15 wherein the plurality of longitudinal channels includes at least 20 longitudinal channels.
 17. The strand anchor as recited in claim 16 wherein the plurality of longitudinal channels includes at least 30 longitudinal channels.
 18. The strand anchor as recited in claim 1 further comprising a plurality of individual wires and at least one spacer, the individual wires being held concentrically with respect to the strand by the at least one spacer.
 19. The strand anchor as recited in claim 18 wherein the individual wires are arranged at a distance from the strand.
 20. The strand anchor as recited in claim 1 wherein the strand anchor is a mining strand anchor.
 21. The strand anchor as recited in claim 1 wherein the at least one longitudinal channel includes a plurality of longitudinal channels.
 22. A method for setting a strand anchor comprising the following steps: drilling a hole into rock; inserting a strand of the strand anchor into the drilled hole; injecting curable material into the drilled hole in the area of an entrance of the drilled hole; and discharging from the drilled hole air displaced by the curable material at least partially through at least one longitudinal channel present in the strand.
 23. The method as recited in claim 22 wherein the air flows through a back end of the at least one longitudinal channel at a back end of the strand into the at least one longitudinal channel and through a front end of the at least one longitudinal channel at a front end of the strand.
 24. The method as recited in claim 23 wherein the front end is outside of the drilled hole.
 25. The method as recited in claim 22 wherein after the curable material has been injected into the drilled hole, the curable material is brought into contact with an outside of the strand so that a mechanical connection is established with the strand after the curable material has cured.
 26. The method as recited in claim 25 wherein the strand anchor includes a plurality of individual wires around the strand, and the curable material forms a mechanical connection with an outside of the individual wires and between the strand and the individual wires.
 27. The method as recited in claim 22 wherein, after the curable material has cured, a tensile force is applied to the strand via an anchor head.
 28. The method as recited in claim 27 wherein the curable material is mortar or synthetic resin.
 29. The method as recited in claim 27 wherein the tensile force also is applied to individual wires of the strand anchor surrounding the stand.
 30. The method as recited in claim 22 further comprising, after the hole has been drilled and before the strand has been inserted, inserting a cartridge containing another curable material into the drilled hole.
 31. The method as recited in claim 22 wherein the strand anchor comprises: the strand including a plurality of wires; an anchor head; an anchor plate supported by the anchor head for placement onto rock; the plurality of wires defining the at least one longitudinal channel between the wires of the strand, the at least one longitudinal channel permitting air to be discharged to an outside through the strand through the at least one longitudinal channel when the curable material is injected into the drilled hole.
 32. The method as recited in claim 22 wherein the air is discharged completely.
 33. The method as recited in claim 22 wherein the at least one longitudinal channel includes a plurality of longitudinal channels. 